Drop plug



Patented Nov. 10, 1942 s PATENT OFFICE liunior PLUG Robert N. Miller, Rosemont, and William B. Miller, Altoona, Pa., assignors to The Pennsylvania Railroad Company, Philadelphia, Pa., a corpo ration of Pennsylvania l Y Application March 1, 1941, Serial No. 381,272

` .s Claims. (c1. 12a-504.3)

This invention relates to safety plugs for steam boilers of the type comprising a hollow bodylcomponent with a drop'member normally sustained therein by a fusible bushing adapted to melt and release said member, under a determined pressure, for giving notice that the water in the boiler has lowered to an undesirable level.

Drop members of the above noted species are held in the body components by press-fitting or other assembly means, while relative "creeping is normally prevented by axial compression of the fusible bushing.

The primary object of this invention is to provide a safety plug of the indicated typeembodying refinements whereby the drop member is initially secured concentric with the axis of the body component bore and so retained until the intervening fusible bushing has sufiiclently melted to permit the steam pressure in the boiler `blowing said drop member directly out without any axial misalignment or tilting tendency conducive to sticking or leakage passage of'steam into the lire-box until the drop member is ejected.

Another object is the provision of an improved coldassembled safety plug in which the releasable member is positively retained in place against creeping, until the moment when it is to be blown out.

Subsidiary objects, with ancillary advantages, will hereinafter appear as the nature of the invention is more fully disclosed, said invention consisting essentially in providing the safety plug body component bore with annular serrations and grooves, correspondingly forming the confrontingly surrounding surface of the drop member and', incidental to force tment of the said parts into coactive relation, laterally expanding the intervening fusible sleeve into mutual engagement by horizontally directed compression.

The accompanying sheet of illustrative drawings exemplifies a practical embodiment of this invention, and wherein similar reference characters are applied to corresponding parts in all the views; while the concluding claims more particularly recite the features of novelty over the prior art.

In the drawing:

Fig. 1 is a vertical section through the body component or member included in one typical embodiment of this invention.

Fig. 2 is a similar section with the fusible sleeve and drop plug in initial assembly with fragmentary portions of appropriate securing means indicated by dot-and-dash lines.

l 3 is a complementally tapered Fig. 3 is a corresponding section illustrating the finished plug installed ina boiler crown sheet. Fig. 4 is a bottom plan view of Fig. 1. Fig. 5 is a perspective view of the fusible sleeve.

Fig. 6 is a perspective view of the drop plug.

Fig. l is `an exaggerated scale section taken approximately within the `confines of the dotand-dash rectangle VII in Fig. 3.

In the following detailed explanation of this invention, specific terms will be employed for the sake of clarity, but it is to be understood such terms are used in a descriptive sense only and not for purposes of limitation, each said term being intended to include all technical equivalents which serve in a similar capacity to accomplish an analogous end. y

Referring now more particularly to the embodiment of this invention, shown by Figs. 1,-7 inclusive, the body component of the improved safety or drop plug is comprehensively designated by the numeral I, said component embodying a machined cylindrical portion Z'having an inwardly converging bore 3, andan externally taper threaded part 4 for screw engagement in a correspondingly threaded aperture 5 provided for its reception in the crown sheet 6.

Interiorly of the converging bore 3 are appropriately formed spaced grooves 1, defined by intervening annular serrations 8, preferably of the cross-section best shown in Fig. 7; that is to say each groove 1 subtends an angle of sixtydegrees evenly divided above and below the horizontal with respect to the axis of said bore 3, and a pitch of approximately four one-thousandths of an inch, or twenty-four serrations per inch. The depth of said serrations 8 is conveniently iifteen-thousandths of an inch, whereas the bore 3 is formed with an inward taper of substantially three-quarters of an inch to the foot. The bore of the taper-threaded part 4 includes an inner cylindrical counterbore 9, and an outer rectangular section socket I0, with the diagonally opposing corners angularly filleted at I I.

Adapted for snug engagement in the plug bore fusible bushing I2 of even surrounding thickness and smooth circumferential finish, interiorly and exteriorly, as readily seen from Fig. 5. This bushing I2, as shown to best advantage in Fig. 2, is of a longitudinal dimension substantially approximating that of the bore 3, and it preferably consists of an alloy containing eighty-five per cent lead with fifteen per cent tin.

The solid releasable closure member or drop plug I3 is preferably of brass and a longitudinal taper complemental to that of the fusible bushing bore I 4, but it is of fractionallygreater diameter so that, when said member is initially inserted in said bore I4, it approximately Voccupies the position shown in Fig. 2, for a purpose later explained. In addition, the surrounding surface of the releasable member or drop plug I3 is formed with annular serrations I5, and grooves I6 in section, conformatory with and alternatingly related to those of the annular body portion bore 3, when said plug is fully inserted, as clearly understandable from an examination of Figs. 3 and 7.

In assembling the plugs I as described, it will be readily understood that the body portion 4 is placed over a suitable stationary die I1, Fig. 2

for example, freely fitting the counterbore 9 and` in abutment with the bottom of the taper ,bored portion 2, when the fusible bushing I2 is insertedV in .the bore 3 with its smaller end also seating on said die. The releasable member or solid drop plug I3 is next inserted in the bore ill of the bushing I2, as shownvin Fig. 2, whereupon the movable die I8 is brought into engagement with the larger end I9 of said die and axially forced, in any conventional manner, towards the stationaryy die I1, with resultant surroundingV interior and exterior lateral and progressive compression of the fusible bushing I2, into coaction with the respective confronting grooves I6 and l, whereby said bushing is caused to firmly interlock with the body portion annu lar serrations 8 as well as the drop plug similar serrations I5. Incidental to such press-ttilng of the parts I, I2 and I5 together in the manner just explained, it will be clearly apparent that no burr is formed either at the top or bottom of the bore 3, or around the upper and lower ends of the releasable drop plugl I 3.

From the foregoing it will be `apparent that, the releasable member or drop plug I3 is firmly interlocked concentric within the body member bore 3, by lateral compressive expansion, outwardly and inwardly, of the fusible sleeve into the longitudinally spaced groovesvI flanking the an- I rations 8, the drop plug I3 is normally retained coaxial with the bore 3 until approaching the blow-out Ipoint, irrespective of any downward movement incidental to softening and progressive melting of the fusible sleeve I2 prior to its forced ejection into the lire-box.

4Having thus described our invention, we claim:

1. In a drop plug, a body component including a cylindrical lsection having the bore defined byk axially-spaced annular serrations and intervening grooves throughout its entire length; a releasable closure member with circumscribing complemental spaced serrations and grooves; all of said serrations and grooves being individually of a cross-section evenly divided above and below the horizontal in Yrespect to the axis of the plug; and a fusible material yplain bushing pressure engaged intermediate the cylindrical section bore and the closure member. Y

2. The combination of claim l wherein the respective serrations and grooves are of like angular cross-section, and the serrations and grooves of the closure member are alternatingly related in respect to those of the cylindrical section bore.

3. The combination of claim 1 wherein the bore of the cylindrical section inwardly converges and the closure member is of corresponding shape, and said closure member is of fraction-ally greater diameter than the bore of the fusible bushing whereby, when the several parts are press-fitted together, no burr is formed at either end of the cylindrical section bore.

ROBERT N. MILLER. WILLIAM B. MILLER. 

